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ch4-time.md

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Dates & Times

LocalDateTime.now(); //2023-05-14T19:56:29.738748
ZonedDateTime.now(); //2023-05-14T19:56:46.627004+02:00[Europe/Zurich]

ZonedDateTime

2021–10–25T09:13:07.769–05:00[America/New_York]

2023-12-16T14:30:00.000-05:00[America/New_York]

GMT vs UTC

  • GMT - Greenwich Mean Time
  • UTC - Coordinated Universal Time

Duration

jshell> java.time.Duration.ofSeconds(758768437)
$54 ==> PT210769H37S

toString

PT24H : starts with PT

I can't use Duration with LocalDate!

var date = LocalDate.of(2023, 1, 21);
var days = Duration.ofDays(1);
// Unsupported unit: Seconds
//I can NOT use Duration with LocalDate
//Exception in thread "main" java.time.temporal.UnsupportedTemporalTypeException: Unsupported unit: Seconds    
System.out.println(date.plus(days));

Period

Usage Of Period

static vs instance

  • Period.of(): static method (does not chain);
  • Period.plus(): instance, does chain
Period oneDay = Period.ofDays(1);
//this is an instance method, so this I can chain
Period p2 = oneDay.plusDays(2);
//example of chaining
p2 = oneDay.plusYears(2).plusMonths(3).plusDays(5);
System.out.println(p2);  //P2Y3M6D

Period.of() does not chain:

//Only the last method is considered!
Period period = Period.ofYears(1).ofMonths(2).ofDays(1);
System.out.println(period);  //P1D

The Period class does not have methods such as getSeconds(), getMinutes(), getHours().

toString

P1D : starts with P example:

P2Y3M6D

Instant

The Instant class represents a specific moment in time in the GMT time zone.

Instant

Format

YYYY-MM-DDTHH:mm:ss.SSSZ

Example:

2024-03-01T14:02:30.123Z

Creation

Only ZonedDateTime has the toInstant() method.

//from ZonedDateTime
Instant instantZRH = zdtZurich.toInstant();
//with now()
Instant now = Instant.now();  //2024-01-18T11:02:16.628552400Z

parse

Instant instant = Instant.parse("2024-03-01T14:02:30.00Z");
System.out.println(instant); //2024-03-01T14:02:30Z

plus

While an Instant represents a specific moment in time using GMT, Java only allows adding or removing units of DAYS or smaller.

Instant now = Instant.now();
Instant then = now.plus(1, ChronoUnit.DAYS); //    //2024-01-08T07:47:52.101744Z

//adding a year - throws an exception
//Exception in thread "main" java.time.temporal.UnsupportedTemporalTypeException: Unsupported unit: Years
Instant inOneYear = now.plus(1, ChronoUnit.YEARS);

ChronoUnit

between

ZonedDateTime zdt1 = ZonedDateTime.of(date, time, zone);
ZonedDateTime zdt2 = zdt1.plus(1, ChronoUnit.HOURS);
long between = ChronoUnit.HOURS.between(zdt1, zdt2);

ChronoUnit